That's a bit rhetorical - I never like challenging the program's quality with real-life boundary conditions like that. Yes, get rid of the oldest backups to create some space - just check whether you should be archiving them somewhere first!

A routine script to archive/delete the oldest file after backing up might be useful - assuming of course that it behaves sensibly if the archive medium is full!

"Klinger, do you know how many zoots were killed to make that one suit?" — BJ Hunnicutt, 4077 M*A*S*H